1. Field of the Invention
The present invention relates to a color photographic diffusion transfer process and more particularly it relates to an improved color photographic diffusion transfer process for color photographic materials containing dye developers.
2. Decription of the Prior Art
Diffusion transfer photographic processes using dye developers or compounds which are dyes and developers for silver halide have been reported in many patents including U.S. Pat. No. 2,983,606 and British Patent No. 804,971. In these processes, as described in the specifications thereof, an exposed photosensitive silver halide emulsion layer is developed in the presence of a dye developer, whereby an imagewise distribution of the unreacted and unoxidized dye developer is formed as a function of the development. The unreacted and unoxidized dye developer is mobile in the processing solution and at least a part of the imagewise distributed dye developer is transferred to a superposed image-receiving element.
In a specific embodiment of the above-described diffusion transfer processes, a photosensitive element having a silver halide emulsion and a dye developer is exposed and a liquid processing composition is applied to the photosensitive element by, for instance, immersing, coating, spraying, etc. Before, during, or after the application of the aforesaid liquid processing composition, the photosensitive element is superposed on an image-receiving element which can be dyed with the dye developer. In a preferred embodiment, the photosensitive element contains the dye developer in a layer adjacent to the side of a silver halide emulsion layer away from the incident light. The silver halide emulsion layer of the photosensitive element is placed on the image-receiving layer of the image-receiving element and a liquid processing composition is spread as a thin layer between the two layers. The liquid processing composition diffuses into the silver halide emulsion layer and the dye developer-containing layer to develope the developable silver halide and the dye developer thus developed the silver halide is immobilized.
This immobilization is apparently due, at least in part, to the reduction is mobility or solubility of the oxidation product of the dye developer as compared with that of the unoxidized dye developer. The immobilization may be also due, at least in part, to the localized reduction of alkali concentration as a function of development.
Since the unreacted dye developer at the nondeveloped areas of the silver halide emulsion layer is diffusible, an imagewise distribution of the mobile unoxidized dye developer is formed as a function of the exposure and development of the silver halide emulsion. At least a part of the diffusible unoxidized dye developer thus imagewise distributed is transferred to the superposed image-receiving layer. This transfer of the unoxidized dye developer is clearly distinguished from the less mobile oxidized dye developer and thus a transferred image is formed on the image-receiving layer.
When a photosensitive element has differently sensitized silver halide emulsion layers and each silver halide emulsion layer is associated with each dye developer which has substantially a complementary color to the main sensitive region of the silver halide emulsion, that is to say, when a silver halide emulsion having sensitivity to red light is associated with a cyar dye developer, a silver halide emulsion having sensitivity to green light with a magenta dye developer, and a silver halide emulsion having sensitivity to blue light with a yellow dye developer, each dye developer is oxidized and immobilized in the developed region or area of each associated silver halide emulsion layer. The dye developers in the nondeveloped portions of the silver halide emulsion layers diffuse and are transferred to the image-receiving element superposed on the photosensitive element.
Therefore, when large proportions of unoxidized dye developers are present in the sufficiently exposed negative portions corresponding to the highlight portions of field or original, they diffuse to an image-receiving element as the unoxidized dye developers present in the nonexposed negative portions corresponding to dark portions of field or original and hence a transferred image having a high minimum density and indistinct light and darkness is formed.
On the other hand, the typical dye developers as disclosed in the specifications of U.S. Pat. Nos. 3,255,001,
______________________________________ 2,992,106; 3,297,441; 3,134,762; 3,236,643; 3,134,673; 3,236,645; 3,134,764; 3,134,672; 3,134,765; 3,183,089; 3,135,734; 3,135,604; 3,173,906; 3,222,169; 3,183,000; 3,201,384; 3,246,985; 3,208,991; 3,142,565; 3,218,312; 3,230,086; 3,262,924; 3,275,617; 3,077,402; 3,282,913; 3,141,772; 3,299,041; 3,309,199; 2,983,605; 3,047,386; 3,076,820; 3,173,929; 3,230,083; 3,236,864; 3,239,339; 3,252,969; 3,253,001; 3,288,778; 3,209,016; 3,135,606; 3,076,808; 3,126,280; 3,236,865; 3,135,605; 3,255,205; 3,131,061; 3,347,673; 3,347,672; 3,246,016; 3,245,790; 3,086,005 3,295,973; ______________________________________
3,307,947; 3,230,082; 3,230,085; etc. for instance, such cyan dye developers as 1,4-bis-(.alpha.-methyl-.beta.-hydroxynonylpropylamino)-5,8-dihydroxyanthr aquinone, etc., such magenta dye developers as 4-propoxy-2-[p-(.beta.-hydroquinonylethyl)-phenylazo]-1-naphthol, etc., and such yellow dye developers as 1-phenyl-3-N-n-hexylcarboxyamido-4-[p-2',5'-dihydroxyphenethyl) phenylazo]-5 -pyrazolone, etc., are weak developing agents for silver halides even when they are used in a comparatively highly alkaline state of a pH of about 1.3. Accordingly, when such conventional dye developers are used, the desired maximum density, gradation, and sensitivity cannot be obtained. Since the immobilization of the dye developers occurs as a function of the development of silver halide emulsion layers, the transferred image obtained in the diffusion transfer process shows undesirably high minimum density, low maximum density, and low contrast in the highlight regions.
This is due, in part, to the fact that the dye developers have weak development activity as a developing agent for silver halide, to the fact that the dye developers near silver are not completely effectively used, and also to other factors.
Furthermore, in a multicolor system it happens that a silver halide emulsion layer is developed not only by the dye developer having substantially complementary color to the main sensitive region of the silver halide emulsion but also by other dye developers associated with other silver halide emulsion layers. For instance, a magenta dye developer which is associated with a green-sensitive silver halide emulsion layer diffuses partially into a blue-sensitive emulsion layer and a red-sensitive emulsion layer to initiate development and is immobilized there, which results in forming a transferred image containing less magenta dye.
In the specifications of Japanese Patent Publication Nos. 4839/1960, 10240/1959, and 2241/1962, the disclosures are that by adding a colorless auxiliary developer such as 1-phenyl-3-pyrazolidone to a processing composition, the development of the silver halide is accelerated and the immobilization of the dye developers in the photosensitive element is accelerated improving to some extent the above-mentioned disadvantage. Also, the use of a hydroquinone such as 4'-methylphenyl hydroquinone as an auxiliary developing agent is described in the specifications of Japanese Patent Publication Nos. 29130/1964 and 13837/1968 and the use of a catechol such as 4-methylcatechol as an auxiliary developing agent is described in the specification of British Patent No. 1,243,539. However, the improvements attained by the above-described inventions are not yet satisfactory and when, in particular, those auxiliary developing agents are used in multicolor-type multilayer photographic elements, it is difficult to obtain satisfactory multicolor transferred images since each dye developer does not cause the development to the necessary extent and also does not cause the development so that the dye developer is fixed in the rate necessary for each specific layer. Still further, it has frequently been observed that a part of the auxiliary developing agents is transferred to an image receiving element causing stains of the color images.